1. Field of the Invention
This invention relates generally to a controller for a fan, such as a fan used in a heating, ventilating, and air conditioning (“HVAC”) system. More specifically, the invention comprises a control system for shutting down the fan of a HVAC system upon detection of an audible alarm, such as a smoke alarm or an alarm from a carbon monoxide detector.
2. Description of the Related Art
HVAC systems pose significant concerns for the safety of the occupants of a house in the case of a fire. The operation of the fan of the HVAC system during a fire produces at least two undesirable consequences. First, the fan circulates smoke to regions of the house which are not directly affected by the fire. This can decrease the response time that the occupants have to evacuate safely from the house. Second, the fan can increase the supply of oxygen to the fire, thereby causing the fire to spread more rapidly. Even worse, the heat generated by a fire can cause the fan of an HVAC system to operate at maximum flow when operating the cooling mode, creating a devastating positive feedback situation.
Several control systems have been made to address these concerns, but the success of these systems has been limited because the systems are overly complicated and/or impractical to implement. One example is U.S. Pat. No. 5,477,913 to Polk. Polk describes a system for disabling a heating/cooling unit when the presence of gases at undesirable levels is detected, or when a smoke alarm has sounded. To accomplish this end, the system utilizes numerous logic circuit elements to disable the heating/cooling operation.